1. Field of the Invention
The present invention relates to a reforming apparatus, for use in a fuel cell, which reforms raw fuel into a reformed gas used in a fuel cell system.
2. Description of the Related Art
A polymer electrolyte fuel cell (PEFC) produces electric power by converting chemical energy of hydrogen into electric energy. For practical purposes, the hydrogen used as a fuel for the polymer electrolyte fuel cell is obtained in a manner that a hydrocarbon gas, such as natural gas or naphtha relatively easily procurable at a relatively low cost, or a raw fuel gas of an alcohol type, such as methanol, and steam are mixed together and then reformed by a reformer. The hydrogen gas obtained by the reforming is supplied to a fuel electrode of the fuel cell and used to generate electricity.
A reformer is generally provided with a burner for supplying the heat required for the reforming reaction of the raw fuel through steam. Combustion gas produced by combusting the fuel by the burner is led from a combustion cylinder to a pathway provided in the vicinity of a reforming reaction unit. As a result, the thermal energy of the combustion gas is used for the reforming reaction.
As an odorant to facilitate the detection of a gas leakage, an organosulfur component is added to the utility gas or propane gas used as the raw fuel gas. When the utility gas, propane gas or the like containing the organosulfur component is directly supplied to the reformer, the organosulfur component is adhered to catalyst in the reformer, thus deteriorating the reforming performance of the reformer. Accordingly, a reforming apparatus provided with a desulfurizer has been conceived.
However, in a conventional reformer, a combustion exhaust gas generated by the fuel combustion in the burner flows inside the reformer and thereby the thermal energy of the combustion exhaust gas is used to generate high-temperature steam or to raise the temperature of the reformer. As a result, the reformer must be placed outside a combustion exhaust gas passage. Also, a shift reactor or a carbon monoxide remover for reducing the carbon monoxide contained in the reformed gas produced by the reformer is placed further outside a passage having the reformer therein. As a result, the passage gets complicated. Therefore, the diameter of the reformer becomes larger and at the same time the reforming apparatus as a whole becomes complicated, thus contributing to an increased size thereof.
Also, in the conventional reformer, the combustion exhaust gas flows inside the reformer only. Hence, there is still room for further improvement in thermal efficiency.
Also, in view of the reforming efficiency in generating the hydrogen, which is a fuel for a fuel cell, from the raw fuel such as the utility gas, it is required that more of the heat of the combustion exhaust gas or reformed gas be used inside the reformer for the generation of steam or the reaction in the reformer.
Also, in the conventional reformer, the catalyst required for the reforming reaction or the reduction of carbon monoxide is placed at a desired position of the reforming reaction unit. However, in the aforementioned reformer, the passage for the reformed gas is still complicated and, at the same time, different catalysts need to be placed in a plurality of passages. Hence, the process of operation is cumbersome and complicated, thus causing a cost increase in manufacturing the apparatus.
Also, if a desulfurizing function is to be added to such a reformer as the above, the structure thereof will be further complicated.
A conventional reformer is a desulfurizing device employing a so-called hydrodesulfurization (HDS) method (hereinafter referred to as “hydrogenation sulfurization method” also) where the raw fuel containing impurities such as sulfur is reacted with hydrogen in the presence of catalyst so as to remove sulfur components. Accordingly, some way to supply the hydrogen to the desulfurizing device must be adopted.